Congress in 2006 required Senate confirmation of the ATF director. But the Senate has never confirmed anyone to serve in the position.

The committee's ranking member, Sen. Chuck Grassley, R-Iowa, reiterated his concerns about Jones' appointment during Thursday's vote in light of an unresolved complaint that Jones retaliated against a whistleblower in Minnesota, where Jones serves as U.S. attorney in addition to holding his interim ATF position.

Grassley said it was "premature'' to proceed with Jones' nomination while he remains the subject of an open investigation, claiming that there was "no genuine effort'' by the committee's Democratic majority "to gather all of the facts.''

Grassley added that he was "concerned about Mr. Jones' leadership ability'' and dubious of promoting him to head the agency.

Grassley grilled Jones during his confirmation hearing last month, questioning whether ATF had punished proponents of the Fast and Furious gunwalking operation, in which Phoenix-based ATF agents were told to stand by while traffickers smuggled weapons to a Mexican drug cartel.

Fast and Furious exploded into scandal when two of the weapons were found at the murder scene of a Border Patrol agent in Arizona in 2010.

In response, Jones testified that he found an "agency in distress'' that was plagued by "poor morale'' when he arrived in the wake of the scandal. He thereafter replaced the bureau's senior managers and special agents in charge of ATF's 25 field divisions.

Sen. Amy Klobuchar, D-Minn., who worked closely with Jones during his tenure as U.S. Attorney in the 1990s and chaired Jones's hearing, added to his defense during Thursday's vote. She countered that "something is wrong when the Senate fails to confirm the head of an agency for seven years.''

"I am concerned that we couldn't confirm anyone for this position if we can't confirm Mr. Jones,'' Klobuchar said during the meeting.

President Barack Obama nominated Jones in January as part of his 23 executive actions to combat gun violence in response to last December's Sandy Hook Elementary School shooting in Newtown, in which 26 children and staff were killed.

Sen. Dianne Feinstein, D-Calif., characterized the opposition to Jones as part of Republicans' "concerted effort to weaken'' the agency.

Grassley conceded that "you might generally say that some Republicans don't want anybody to be confirmed for ATF," but he insisted that he was not among them and was protecting the rights of whistleblowers.

Sen. John Cornyn, R-Texas, said that he would not vote to move Jones' nomination forward, citing Jones' "troubling track record'' and "lack of leadership and accountability.''

"As a committed defender of Texans' Second Amendment rights, I have serious concerns that Mr. Jones would infringe on these rights,'' Cornyn said.